This invention relates to clean room ceilings and more particularly to filter assemblies for clean rooms which provide for near 100% active filter surface of the ceiling and which eliminates the need for conventional ceiling grid support systems.
In recent years, the development of clean rooms has necessarily preceeded the quantity manufacture of precision electronics and aerospace products. In particular, virtually all high technology companies require that precision activities be conducted in a dust or contaminent free clean room, i.e. one with filtered air having laminar flow from the ceiling to lower level returns with all of the air introduced into the ceiling via a plenum area above an array of filters which provide the laminar flow of filtered air.
Characteristically, rather elaborate grid structures have been required to support the filters. The grid structures nor only have the support function which is similar to suspended office type ceiling but the grid systems themselves must have air tight joints to avoid leakage of unfiltered air into the otherwise clean room. Additionally, the grid structure customarily must support auxiliary services such as lighting fixtures and sprinklers. These auxiliary devices and the grid itself present not only air leakage dangers but reduce the overall laminar flow characteristics of the system. Usually a section of filters must be eliminated in order to provide a dummy section in which the auxiliary services such as lighting and sprinklers are installed.
Examples of typical clean room ceiling suspension systems are illustrated in the following patents:
______________________________________ U.S. Pat. No. Issue Date Inventor ______________________________________ 3,782,082 Jan. 1,1974 Smith et al 3,986,850 Oct. 19,1976 D. E. Wilcox 4,570,391 Feb. 18, 1986 Quante et al 4,710,028 Dec. 1,1987 Ziemer et al ______________________________________
The Wilcox U.S. Pat. No. 3,986,850 illustrates attempts to place rows of lighting fixtures 53 between banks of filters 49. As is apparent, the rows of lighting fixtures 53 reduce the overall filtered area of the ceiling and prevent any laminar flow directly beneath the fixtures.
Similar alternate filter and light assemblies supported by a grid are illustrated in U.S. Pat. No. 4,603,618 to C. W. Soltis issued Aug. 5, 1986. In an attempt to minimize a disturbance of the laminar flow, the Soltis patent shows a diffusion panel below the filters and the lighting fixtures.
The importance of ceiling filters and the ceiling grid has been indicated above and the effective seals have bee achieved in the past employing troughs in the framework which are filled with a viscous gel and into which a depending edge of a filter assembly extends coated with the gel. An airtight seal is thereby produced between a filter panel and the supporting frame. Examples of the use of such viscous gel seals are shown in U.S. Pat. No. 3,986,850 to Wilcox, Reissue patent No. 27,701 to Cadwell, a reissue of U.S. Pat. No. 3,529,406 and perhaps the earliest disclosure of gel seals in a clean room channel suspension system appears in U.S. Pat. No. 3,486,311 to A. R. Allen Jr., issued Dec. 30, 1969.
Despite the 20 years of development of clean rooms the following objectives have yet to be achieved:
(1) Elimination of the loss of filter area due to the presence of the grid suspension system;
(2) Providing near 100% effective laminar flow area of the ceiling;
(3) Provision for minimum interference with air flow and ease of servicing auxiliary features such as lighting and sprinklers without disturbing the integrity of the filter system;
(4) Ease and simplicity of installation;
(5) Ease of removal and replacement of filter panels with assurance of restoration of ceiling filter integrity and;
(6) Effective location and operation of auxiliary services such as lighting and sprinklers without degradation of their performance by reason of the presence of the filters or the suspension system.
None of these advantages have been achieved employing prior art systems. Examples of other systems beside those described above which likewise fail to achieve these results are the following:
______________________________________ U.S. Pat. No. Issue Date Inventor ______________________________________ 4,554,766 Nov. 26, 1985 Ziemer et al 4,549,472 Oct. 29, 1985 Endo et al 4,671,811 June 9, 1987 Cadwell et al 4,461,205 July 24, 1984 Shuler 3,626,837 Jan. 1, 1974 Smith et al 3,935,803 Feb. 3, 1976 L. Bush 3,688,477 Sept. 5, 1972 C. Coward Jr. 4,082,525 April 4, 1978 T. T. Allan 4,088,463 May 9, 1978 I.M. Smith ______________________________________